Read, reblog, and resonate!
The name would be "Anomaly Completion"
The Idea of the Au came to me when i realized even tough frisk is truly a separate character from us,unlike Kris from deltarune who has a backstory of theyre own before we come into play,frisk has NO backstory at ALL
That made me think of the Idea of frisk NOT EXISTING before the events of the game,quite literally the moment we start the Run being the moment they are born
Then after brainstorming a little about How such Idea would interfer with the plot o realized Nothing would changed much,NOT even after the true pacifist ending because the choice to stay with toriel would lead to no conflicts with frisk real parents or Any human civilian because frisk has no connection to those
Then i realized,what If i play the reverse,frisk NOT Only Dint exist before they fall but also they cease to exist after they leave the underground,Thats why neutral runs we get ZERO Idea of what is going on with frisk...
It then hit me,It Gave me a reason for a genocide Run frisk WHITOUT the need of a player interfering or even EXISTING at all in the story
Frisk starts the genocide Run because they need more Power to keep EXISTING,and the easiest and most effective Way to obtain Said Power is a genocide run
I then realized... Wait,WHY would frisk NOT exist before theyre Fall and THEN come into existance out of nowhere and THEN suddenly cease to be From existance once they leave the undeground
I decided then to change the plot reatroactively now... My mind pierced together the clues and made an idea
Gaster,the delta rune Angel's prophecy,the implications the Power of LOVE can make a non corporeal entity more "real" from The end of genocide,the previous fallen children mistérious reasons for why would they come to Mont ebott and the world being sentient implications from The genocide Run(mostly undyne speech and background noise during It from "but the earth refused to die")
And then came the plot
The deltarune was created by gaster long in the past(because he was shattered across space-time the fact he affected something from before his own birth is kinda completely possible),the deltarune Tells the tale of an angel who Falls from The Surface to inevitably free the underground.
The world is sentient,but acts more like a computer kinda of sentient than anything Else,It receive input X then It give output Y,aways,NO exception,gaster abuses that to make the world FORCIBLY try Its best to make the prophecy inevitably comes true,not matter what
It changes things,a Flip or a coin there, gust off Wind here,a bird decides to pick the worm on the left instead of the rigth and soo on,until a giant domino effect brings chara to MT ebbot,the barrier is too powerfull and the world cannot change things inside It in the same Way It does outside of It(undyne's DT allowing It for a brief moment as the exception)
Because the world cant mess with fate inside,It cant stop chara's plan,and the Power of a Monster with a human soul is too big for It to be affected too(they ARE powerfull enough to Cross the barrier,thus more powerfull than It)
Because chara died the prophecy cant come true thus the world has to bring another child into the underground again,thus the reason why they come,but they are killed by asgore,thus the prophecy is Still incomplete
After enough disapearences on MT ebbot,the humans decide to Just straigth UP board UP the entrance to the underground and put a few more barris(not Magic ones) around the area
The world can no longer manipulate fate to being humans there because what It could do had to Still bê in line with what was possible,since entrance to the underground was now COMPLETELY sealed then It was no longer possible and thus the world has to take even more Drastic measures to Follow gaster's prophecy disguised command
It then created a entity,a blob of magical energy not that diferent from a amalgamate Monster,It Falls on top of chara's grave and thus take a form awfully similar to them due to it
Thus
Frisk's existance start,now with the purpose of the deltarune's angel ingraved into theyre Very soul
And the Run can finally start